The present invention relates to a water-in-oil (W/O) type emulsion explosive which can be used for the industrial blasting for various purposes such as, for example, excavation of tunnels, quarrying and mining.
Many improvements and inventions have been made regarding the W/O type emulsion explosives ever since this type of explosive was disclosed for the first time in U.S. Pat. No. 3,161,551. The W/O type emulsion explosives in these inventions are basically of the composition comprising a mineral oil, wax or other hydrophobic carbonaceous fuel (oil) as continuous phase, an aqueous solution of oxidizers mainly composed of ammonium nitrate as discontinuous phase, and a W/O type emulsifier. By properly adding a sensitizer such as hollow microspheres to the composition, there can be obtained the W/O type emulsion explosive of various level of initiating sensitivity ranging from booster initiation to cap initiation. As is well known, these W/O type emulsion explosives, because of use of oily material as continuous phase, are excellent in water resistance and safety in comparison with the conventional explosives.
The W/O type emulsion explosives have the problem that they lack stability since the emulsion is formed by mixing two mutually, insoluble liquids into a homogeneous liquid mixture comprising fine droplets of one liquid in the other liquid with the aid of an emulsifier. Many inventions purposed to improve stability of this type of emulsion explosives have been made. A method for improving stability is to use a specific emulsifier as for instance proposed in Japanese Patent Application Laid-Open (Kokai) Nos. 58-120588 (1983) and 58-190890 (1983) and U.S. Pat. Nos. 4,482,403 and 4,698,105. Use of a specific oil is another method for improving stability of said emulsion explosives, as for instance proposed in Japanese Patent Application Laid-Open (Kokai) Nos. 57-149893 (1982), 61-40892 (1986) and 61-40893 (1986) and U.S. Pat. Nos. 4,386,977, 4,548,660 and 4,470,855.
Stability of the W/O type emulsion explosives was greatly improved by these inventions, and this type of explosives has come to be used widely. However, the W/O type emulsion explosives still have the problem that the sensitivity lowers with the lapse of time, and some of those W/O type emulsion explosives which have been kept in storage for 2 to 3 years fail to detonate in the hole due to insufficient sensitivity.